Repair or replace your HVAC system

The rule most contractors quote is the $5,000 rule: multiply the repair cost by the age of the system, and if it comes to more than $5,000, replace. A $600 repair on a ten year old system is $6,000, so replace.

It is a memorable rule and it is wrong often enough to cost people money. It treats a fifteen year old system with a $300 capacitor as a replacement, which it is not.

Here is a better way to think about it, and the specific situations where the answer is not close.

The arithmetic that actually works

Divide the repair by the years it realistically buys. Compare that to a replacement divided by its expected life.

An $11,000 changeout over fifteen years is about $733 a year. So:

The variable that decides it is not the price of the repair. It is how many years the rest of the system has left, and that is a judgement about the compressor, the coil and the refrigerant type rather than a number anyone can look up.

Replace, and it is not close

• A cracked heat exchanger out of warranty. It is a carbon monoxide risk, and replacing the exchanger costs most of a new furnace and leaves you with an old furnace.
• An R-22 system with a refrigerant leak. The gas is out of production and expensive, and you would be buying it repeatedly for equipment that is at minimum fifteen years old.
• A failed compressor past twelve years, out of warranty. By the time you add labor, refrigerant, a filter drier and finding what killed it, you are past half the cost of a system with a fresh warranty.
• Two significant repairs in two seasons. The third one is coming.
• A system past twenty years facing any repair over about $1,000.

Repair, and it is not close

• The part is under warranty. Almost anything. You pay labor and you get a covered part.
• The system is under about eight years old. It has most of its life left.
• The failure is electrical rather than in the sealed refrigerant loop. Capacitors, contactors, igniters, flame sensors, control boards, thermostats: all cheap relative to the machine.
• You are selling within a year or two. A working system is what you need, and you will not recover the cost of a new one in the sale price.

The middle, and how to decide

Between about ten and fifteen years with a repair in the $1,200 to $2,500 range is where the real decision lives. Four questions:

What refrigerant is it? R-22 tips it to replace on its own. It is printed on the outdoor unit's nameplate.

Has anything else failed recently? One repair on a well-maintained system is different from the third in two years.

What are you actually paying to run it? A fifteen year old 10 SEER system against a modern 15 SEER2 one is roughly a third less electricity for cooling. In a hot climate that is $300 to $600 a year, which changes the arithmetic materially. In a mild one it is $80.

What is the incentive picture right now? The federal energy efficiency credit returns up to $2,000 on a qualifying heat pump and up to $600 on a qualifying air conditioner or furnace, and many utilities add rebates. Two thousand dollars off a replacement moves a lot of borderline cases.

Get the diagnosis before the decision

The mistake that costs the most is accepting a replacement recommendation without knowing what failed.

Ask, and write down:

• Which specific part failed, and what it costs to replace
• How it was diagnosed, and what was measured
• The model and serial number of the equipment, and its manufacture date
• The warranty status, which you can check yourself on the manufacturer's website
• What the replacement quote includes: tonnage, model numbers, ductwork, permit, labor warranty

Then get a second opinion, particularly if the first visit was free. A free diagnostic is a sales call, and sometimes it is also an honest diagnosis, but you cannot tell which from inside the conversation.

Frequently asked questions

Is the $5,000 rule useless?

Not useless, but blunt. It is roughly right in the middle of the range and wrong at both ends: it says replace a fifteen year old system over a $350 capacitor, and it says repair a nine year old one facing a $500 compressor that does not exist.

Should I replace the furnace and air conditioner together?

If both are over about twelve years, yes. The indoor coil sits on the furnace, so doing them separately means opening the refrigerant system twice and paying much of the same labor twice. Together typically saves $800 to $1,200.

The contractor says parts are no longer available. Is that true?

Sometimes genuinely, on equipment past about twenty years or from a manufacturer no longer trading. It is also a common line. Ask for the part number, and search it.

Will a home warranty decide this for me?

It will try to. Most policies prefer the cheapest repair that restores function and cap payouts below the cost of a compressor. That is not the same as the decision that is right for you.

If I replace, how long should the new one last?

Fifteen to twenty years for an air conditioner or heat pump, fifteen to twenty-five for a gas furnace. Sizing, installation quality and annual maintenance move that more than brand does.